The present invention generally concerns air purification, and more specifically, the purification of air that contains toxic species, using high-temperature processing.
In recent years, there has been considerable concern by the military that troops may enter war zones and be exposed to air contaminated with toxic chemical and/or biological agents. Examples of such toxic chemical agents include Sarin, mustard gas (bis(2-chloroethyl)thioether), phosgene, and cyanogen chloride; examples of biological agents include Anthrax, E. coli, Salmonella, Hepatitis, and Norwalk virus. Although outlawed by worldwide treaties, the use of such warfare agents in military conflicts is a strong possibility and poses a serious threat to both military and civilian personnel.
There are several known methods for removing or destroying chemical species from contaminated air, including adsorption by carbon, photo-catalytic oxidation and thermocatalytic oxidation. In addition, methods for removing or destroying airborne bacteria particulates include filtration, photo-catalytic oxidation, and thermocatalytic oxidation. Apparatus useful for employing these methods are also well known in the art.
While the foregoing methods (and their associated apparatus) are suitable in certain instances, they may not produce viable results in the field under warfare conditions. For example, a specific air filtration device may remove certain types of toxic biological species, such as bacteria, while not removing other toxic species, such as viruses, or may not be able to reduce the concentration level of a particular toxic species to an acceptable level. Furthermore, the devices used to implement the methods may require heavy or bulky equipment that is impractical for use by personnel in the field, who need to be provided with lightweight devices. It would therefore be desirable to provide a compact air purification device capable of removing and/or reducing toxic warfare agents to an acceptable level that can be worn or used by ground troops and others who may be exposed to these agents.
Another problem that is frequently encountered is the unknowing consumption of food containing toxic species such as E. coli, Salmonella, or Hepatitis. Each of these toxins can be harmful when ingested by humans, causing death in some circumstances. Food is sometimes contaminated with these toxins during food processing operations, or may be contaminated through contact with air containing such toxins, due to inadequate sealing of the food and/or inadequate refrigeration, or prolonged refrigeration. For instance, raw eggs commonly are infected with Salmonella, and E. coli is often found in animal waste and can contaminate meat processed in plants that apply inadequate or improper procedures. Additionally, unpasteurized fruit products such as fruit juices may be contaminated with E. coli if made with fruit that has come into contact with animal waste. Furthermore, ethylene oxide and other chemical contaminants increase the rate at which food spoils in confined spaces such as refrigerators. It would therefore be desirable to provide apparatus for purifying air in food processing plants, cold storage facilities, and refrigerators; the apparatus should be capable of removing or deactivating a substantial portion of any toxic species present in the air in such facilities. It would also be beneficial to provide a similar device for removing ammonia, amines, and other organic chemicals for the air in semiconductor processing plant environments.
The present invention addresses the foregoing problems by providing a process and associated apparatus for purifying air that is particularly useful in removing or deactivating toxic chemical and biological species such as Sarin, mustard gas, phosgene, cyanogen chloride, ammonia, ethylene oxide, Anthrax spores, E. coli bacteria, salmonella bacteria, Hepatitis virus, listeria, legionella, and Norwalk virus. The apparatus can be configured in different embodiments, including those that employ a noble metal catalyst to facilitate a thermocatalytic deactivation of a vast majority of the toxic chemical and biological species present in the air. One or more embodiments is sufficiently portable for use on the battlefield, and other embodiments for removing toxic species from areas in which food is prepared or stored.
According to a first aspect of the invention, air purification apparatus include a thermocatalytic reactor coupled to a counterflow heat exchanger. The thermocatalytic reactor has an enclosed passage with a surface area comprising a noble metal catalyst over which heated air is directed to flow. The noble metal catalyst promotes a thermocatalytic reaction that deactivates at least 90% of any toxic chemical and biological species present in the air. The counterflow heat exchanger greatly increases the thermal efficiency of the process by substantially heating the contaminated air that enters the apparatus and cooling the air that leaves the thermocatalytic reactor so that the air is nearly at ambient temperature when it exits the apparatus. The noble metal catalyst preferably is platinum, or palladium, or a combination of the two. The air is preferably heated to at least 200xc2x0 C., and more preferably to at least 300xc2x0 C., using an electric resistance heater, or a light hydrocarbon combustor, or other heat source. The apparatus is especially well suited for removing and/or deactivating toxic species having a size less than 10 xcexcm and a concentration level less than 50,000 parts per million (ppm).
According to a second aspect of the invention is directed to portable air purification apparatus incorporating substantially the same components as the foregoing apparatus, but in a reduced size. Included is a reaction chamber in which the air is preferably heated to a sufficient temperature to deactivate toxic biological species commonly associated with food poisoning, such as salmonella bacteria and E. coli bacteria. The portable apparatus may optionally include a catalyst element that is suited for use in the thermocatalytic deactivation of toxic warfare agents, such as nerve gases and chemical agents. The counterflow heat exchanger preferably comprises a plurality of thin plates that are stacked in an alternating fashion such that heat is exchanged between an incoming stream of contaminated air and an exiting stream of purified air, in a counterflow heat exchanger configuration.
According to further aspects of the invention, various scavenger apparatus are disclosed for purifying larger quantities of air, such as in a food processing plant or clean room. The scavenger apparatus comprise various external configurations, including cylindrical and cubic shapes. Included is a counterflow heat exchanger in fluid communication with a reaction chamber in which contaminated air is thermally and/or thermocatalytically deactivated, in the manner discussed above.
According to another aspect of the invention, a process for purifying air contaminated with toxic biological and/or chemical species is defined. The process can be implemented with the foregoing apparatus, and begins by directing contaminated air, e.g., from the ambient, through a heating fluid path through a counterflow heat exchanger, wherein the air is heated to a temperature substantially above ambient. The air is preferably heated to at least 200xc2x0 C., and more preferably to at least 300xc2x0 C., whereupon it is passed over a surface comprising a noble metal catalyst. The catalyst purifies the air by creating a thermocatalytic reaction that deactivates a substantial portion of the toxic biological and chemical species present in the air. The purified air is then directed along a cooling path through the counterflow heat exchanger and cooled by heat transfer with the air eitering the apparatus. The temperature of the purified air exiting the heat exchanger is close to ambient.